Butyl-bridged diphosphine ligands for alkoxycarbonylation

ABSTRACT

The invention relates to compounds of formula (I)whereR1, R2, R3, R4 are each independently selected from —(C1-C12)-alkyl, —(C3-C12)-cycloalkyl, —(C3-C12)-heterocycloalkyl, —(C6-C20)-aryl, —(C3-C20)-heteroaryl;at least one of the R1, R2, R3, R4 radicals is a —(C3-C20)-heteroaryl radical;andR1, R2, R3, R4, if they are —(C1-C12)-alkyl, —(C3-C12)-cycloalkyl, —(C3-C12)-heterocycloalkyl, —(C6-C20)-aryl or —(C3-C20)-heteroaryl,may each independently be substituted by one or more substituents selected from —(C1-C12)-alkyl, —(C3-C12)-cycloalkyl, —(C3-C12)-heterocycloalkyl, —O—(C1-C12)-alkyl, —O—(C1-C12)-alkyl-(C6-C20)-aryl, —O—(C3-C12)-cycloalkyl, —S—(C1-C12)-alkyl, —S—(C3-C12)-cycloalkyl, —COO—(C1-C12)-alkyl, —COO—(C3-C12)-cycloalkyl, —CONH—(C1-C12)-alkyl, —CONH—(C3-C12)-cycloalkyl, —CO—(C1-C12)-alkyl, —CO—(C3-C12)-cycloalkyl, —N—[(C1-C12)-alkyl]2, —(C6-C20)-aryl, —(C6-C20)-aryl-(C1-C12)-alkyl, —(C6-C20)-aryl-O—(C1-C12)-alkyl, —(C3-C20)-heteroaryl, —(C3-C20)-heteroaryl-(C1-C12)-alkyl, —(C3-C20)-heteroaryl-O—(C1-C12)-alkyl, —COOH, —OH, —SO3H, —NH2, halogen;and to the use thereof as ligands in alkoxycarbonylation.

The invention relates to butyl-bridged diphosphine compounds, to metalcomplexes of these compounds and to the use thereof foralkoxycarbonylation.

The alkoxycarbonylation of ethylenically unsaturated compounds is aprocess of increasing significance. An alkoxycarbonylation is understoodto mean the reaction of ethylenically unsaturated compounds (olefins)with carbon monoxide and alcohols in the presence of a metal-ligandcomplex to give the corresponding esters. Typically, the metal used ispalladium. The following scheme shows the general reaction equation ofan alkoxycarbonylation:

Among the alkoxycarbonylation reactions, particularly the reaction ofethene and methanol to give 3-methylpropionate (ethenemethoxycarbonylation) is of significance as an intermediate step for thepreparation of methyl methacrylate (S. G. Khokarale, E. J.Garcïa-Suárez, J. Xiong, U. V. Mentzel, R. Fehrmann, A. Riisager,Catalysis Communications 2014, 44, 73-75). Ethene methoxycarbonylationis conducted in methanol as solvent under mild conditions with apalladium catalyst modified by phosphine ligands.

Typically, bidentate diphosphine compounds are used here as ligands. Avery good catalytic system was developed by Lucite—now MitsubishiRayon—and uses a ligand based on1,2-bis(di-tert-butylphosphinomethyl)benzene (DTBPMB) (W. Clegg, G. R.Eastham, M. R. J. Elsegood, R. P. Tooze, X. L. Wang, K. Whiston, Chem.Commun. 1999, 1877-1878).

EP 0975574 A1 discloses the carbonylation of 3-methoxy-1-butene to givemethyl 3-pentenoate in the presence of, for example,1,4-bis(diphenylphosphino)butane and1,4-bis(dicyclohexylphosphino)butane. The carbonylation of long-chainethylenically unsaturated compounds, such as octene for example, is notexamined.

1,4-Bis(dialkylphosphino)butane compounds are also used in other sectorsas ligands for palladium catalysts. For example, WO 02/10178 disclosesthe use of 1,4-bis(diadamantyl-phosphino)butane as a ligand for addingvalue to haloaromatics and for production of arylolefins, dienes,diaryls, benzoic acid and acrylic acid derivatives, arylalkanes andamines. However, there is no description of the use of these ligands foralkoxycarbonylation.

The problem addressed by the present invention is that of providingnovel ligands for alkoxycarbonylation, with which good yields of esterscan be achieved. More particularly, the ligands according to theinvention are to be suitable for the alkoxycarbonylation of long-chainethylenically unsaturated compounds, for example C₈ olefins, and ofmixtures of ethylenically unsaturated compounds.

This problem is solved by butyl-bridged diphosphine compoundssubstituted by at least one heteroaryl radical on at least onephosphorus atom. These compounds are particularly suitable as bidentateligands for palladium complexes and lead to elevated yields in thealkoxycarbonylation of ethylenically unsaturated compounds, especiallyof C₈ olefins.

The diphosphine compounds according to the invention are compounds offormula (I)

where

R¹, R², R³, R⁴ are each independently selected from —(C₁-C₁₂)-alkyl,—(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —(C₆-C₂₀)-aryl,—(C₃-C₂₀)-heteroaryl;

at least one of the R¹, R², R³, R⁴ radicals is a —(C₃-C₂₀)-heteroarylradical;

and

R¹, R², R³, R⁴, if they are —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl,—(C₃-C₁₂)-heterocycloalkyl, —(C₆-C₂₀)-aryl or —(C₃-C₂₀)-heteroaryl,

may each independently be substituted by one or more substituentsselected from —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl,—(C₃-C₁₂)-heterocycloalkyl, —O—(C₁-C₁₂)-alkyl,—O—(C₁-C₁₂)-alkyl-(C₆-C₂₀)-aryl, —O—(C₃-C₁₂)-cycloalkyl,—S—(C₁-C₁₂)-alkyl, —S—(C₃-C₁₂)-cycloalkyl, —COO—(C₁-C₁₂)-alkyl,—COO—(C₃-C₁₂)-cycloalkyl, —CONH—(C₁-C₁₂)-alkyl,—CONH—(C₃-C₁₂)-cycloalkyl, —CO—(C₁-C₁₂)-alkyl, —CO—(C₃-C₁₂)-cycloalkyl,—N—[(C₁-C₁₂)-alkyl]₂, —(C₆-C₂₀)-aryl, —(C₆-C₂₀)-aryl-(C₁-C₁₂)-alkyl,—(C₆-C₂₀)-aryl-O—(C₁-C₁₂)-alkyl, —(C₃-C₂₀)-heteroaryl,—(C₃-C₂₀)-heteroaryl-(C₁-C₁₂)-alkyl,—(C₃-C₂₀)-heteroaryl-O—(C₁-C₁₂)-alkyl, —COOH, —OH, —SO₃H, —NH₂, halogen.

The expression (C₁-C₁₂)-alkyl encompasses straight-chain and branchedalkyl groups having 1 to 12 carbon atoms. These are preferably(C₁-C₈)-alkyl groups, more preferably (C₁-C₆)-alkyl, most preferably(C₁-C₄)-alkyl.

Suitable (C₁-C₁₂)-alkyl groups are especially methyl, ethyl, propyl,isopropyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, n-pentyl,2-pentyl, 2-methylbutyl, 3-methylbutyl, 1,2-dimethylpropyl,1,1-dimethylpropyl, 2,2-dimethylpropyl, 1-ethylpropyl, n-hexyl, 2-hexyl,2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1,1-dimethylbutyl,1,2-dimethylbutyl, 2,2-dimethylbutyl, 1,3-dimethylbutyl,2,3-dimethylbutyl, 3,3-dimethylbutyl, 1,1,2-trimethylpropyl,1,2,2-trimethylpropyl, 1-ethylbutyl, 1-ethyl-2-methylpropyl, n-heptyl,2-heptyl, 3-heptyl, 2-ethylpentyl, 1-propylbutyl, n-octyl, 2-ethylhexyl,2-propylheptyl, nonyl, decyl.

The elucidations relating to the expression (C₁-C₁₂)-alkyl also applyparticularly to the alkyl groups in —O—(C₁-C₁₂)-alkyl,—S—(C₁-C₁₂)-alkyl, —COO—(C₁-C₁₂)-alkyl, —CONH—(C₁-C₁₂)-alkyl,—CO—(C₁-C₁₂)-alkyl and —N—[(C₁-C₁₂)-alkyl]₂.

The expression (C₃-C₁₂)-cycloalkyl encompasses mono-, bi- or tricyclichydrocarbyl groups having 3 to 12 carbon atoms. Preferably, these groupsare (C₅-C₁₂)-cycloalkyl.

The (C₃-C₁₂)-cycloalkyl groups have preferably 3 to 8, more preferably 5or 6, ring atoms.

Suitable (C₃-C₁₂)-cycloalkyl groups are especially cyclopropyl,cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl,cyclododecyl, cyclopentadecyl, norbornyl, adamantyl.

The elucidations relating to the expression (C₃-C₁₂)-cycloalkyl alsoapply particularly to the cycloalkyl groups in —O—(C₃-C₁₂)-cycloalkyl,—S—(C₃-C₁₂)-cycloalkyl, —COO—(C₃-C₁₂)-cycloalkyl,—CONH—(C₃-C₁₂)-cycloalkyl, —CO—(C₃-C₁₂)-cycloalkyl.

The expression (C₃-C₁₂)-heterocycloalkyl encompasses nonaromatic,saturated or partly unsaturated cycloaliphatic groups having 3 to 12carbon atoms, where one or more of the ring carbon atoms are replaced byheteroatoms. The (C₃-C₁₂)-heterocycloalkyl groups have preferably 3 to8, more preferably 5 or 6, ring atoms and are optionally substituted byaliphatic side chains. In the heterocycloalkyl groups, as opposed to thecycloalkyl groups, one or more of the ring carbon atoms are replaced byheteroatoms or heteroatom-containing groups. The heteroatoms or theheteroatom-containing groups are preferably selected from O, S, N,N(═O), C(═O), S(═O). A (C₃-C₁₂)-heterocycloalkyl group in the context ofthis invention is thus also ethylene oxide.

Suitable (C₃-C₁₂)-heterocycloalkyl groups are especiallytetrahydrothiophenyl, tetrahydrofuryl, tetrahydropyranyl and dioxanyl.

The expression (C₆-C₂₀)-aryl encompasses mono- or polycyclic aromatichydrocarbyl radicals having 6 to 20 carbon atoms. These are preferably(C₆-C₁₄)-aryl, more preferably (C₆-C₁₀)-aryl.

Suitable (C₆-C₂₀)-aryl groups are especially phenyl, naphthyl, indenyl,fluorenyl, anthracenyl, phenanthrenyl, naphthacenyl, chrysenyl, pyrenyl,coronenyl. Preferred (C₆-C₂₀)-aryl groups are phenyl, naphthyl andanthracenyl.

The expression (C₃-C₂₀)-heteroaryl encompasses mono- or polycyclicaromatic hydrocarbyl radicals having 3 to 20 carbon atoms, where one ormore of the carbon atoms are replaced by heteroatoms. Preferredheteroatoms are N, O and S. The (C₃-C₂₀)-heteroaryl groups have 3 to 20,preferably 6 to 14 and more preferably 6 to 10 ring atoms. Thus, forexample, pyridyl in the context of this invention is a C₆-heteroarylradical; furyl is a C₅-heteroaryl radical.

Suitable (C₃-C₂₀)-heteroaryl groups are especially furyl, thienyl,pyrrolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, imidazolyl,pyrazolyl, furazanyl, tetrazolyl, pyridyl, pyridazinyl, pyrimidyl,pyrazinyl, benzofuranyl, indolyl, isoindolyl, benzimidazolyl, quinolyl,isoquinolyl.

The expression halogen especially encompasses fluorine, chlorine,bromine and iodine. Particular preference is given to fluorine andchlorine.

In one embodiment, the R¹, R², R³, R⁴ radicals, if they are—(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl,—(C₆-C₂₀)-aryl, or —(C₃-C₂₀)-heteroaryl, may each independently besubstituted by one or more substituents selected from —(C₁-C₁₂)-alkyl,—(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —O—(C₁-C₁₂)-alkyl,—O—(C₁-C₁₂)-alkyl-(C₆-C₂₀)-aryl, —O—(C₃-C₁₂)-cycloalkyl,—S—(C₁-C₁₂)-alkyl, —S—(C₃-C₁₂)-cycloalkyl, —(C₆-C₂₀)-aryl,—(C₆-C₂₀)-aryl-(C₁-C₁₂)-alkyl, —(C₆-C₂₀)-aryl-O—(C₁-C₁₂)-alkyl,—(C₃-C₂₀)-heteroaryl, —(C₃-C₂₀)-heteroaryl-(C₁-C₁₂)-alkyl,—(C₃-C₂₀)-heteroaryl-O—(C₁-C₁₂)-alkyl, —COOH, —OH, —SO₃H, —NH₂, halogen.

In one embodiment, the R¹, R², R³, R⁴ radicals, if they are—(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl,—(C₆-C₂₀)-aryl, or —(C₃-C₂₀)-heteroaryl, may each independently besubstituted by one or more substituents selected from —(C₁-C₁₂)-alkyl,—(C₃-C₁₂)-cycloalkyl, —O—(C₁-C₁₂)-alkyl,—O—(C₁-C₁₂)-alkyl-(C₆-C₂₀)-aryl, —O—(C₃-C₁₂)-cycloalkyl, —(C₆-C₂₀)-aryl,—(C₆-C₂₀)-aryl-(C₁-C₁₂)-alkyl, —(C₆-C₂₀)-aryl-O—(C₁-C₁₂)-alkyl,—(C₃-C₂₀)-heteroaryl, —(C₃-C₂₀)-heteroaryl-(C₁-C₁₂)-alkyl,—(C₃-C₂₀)-heteroaryl-O—(C₁-C₁₂)-alkyl.

In one embodiment, the R¹, R², R³, R⁴ radicals, if they are—(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl,—(C₆-C₂₀)-aryl, or —(C₃-C₂₀)-heteroaryl, may each independently besubstituted by one or more substituents selected from —(C₁-C₁₂)-alkyl,—O—(C₁-C₁₂)-alkyl-(C₆-C₂₀)-aryl, —(C₃-C₂₀)-heteroaryl,—(C₃-C₂₀)-heteroaryl-(C₁-C₁₂)-alkyl,—(C₃-C₂₀)-heteroaryl-O—(C₁-C₁₂)-alkyl.

In one embodiment, the R¹, R², R³, R⁴ radicals, if they are—(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl,—(C₆-C₂₀)-aryl, or —(C₃-C₂₀)-heteroaryl, may each independently besubstituted by one or more substituents selected from —(C₁-C₁₂)-alkyland —(C₃-C₂₀)-heteroaryl.

In one embodiment, the R¹, R², R³, R⁴ radicals are unsubstituted if theyare —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, or—(C₃-C₁₂)-heterocycloalkyl, and may be substituted as described if theyare —(C₆-C₂₀)-aryl, or —(C₃-C₂₀)-heteroaryl.

In one embodiment, the R¹, R², R³, R⁴ radicals are unsubstituted if theyare —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl,—(C₆-C₂₀)-aryl, or —(C₃-C₂₀)-heteroaryl.

In one embodiment, R¹, R², R³, R⁴ are each independently selected from—(C₁-C₁₂)-alkyl, —(C₆-C₂₀)-aryl, —(C₃-C₂₀)-heteroaryl;

where at least one of the R⁴, R², R³, R⁴ radicals is a—(C₃-C₂₀)-heteroaryl radical;

and R¹, R², R³, R⁴, if they are —(C₁-C₁₂)-alkyl, —(C₆-C₂₀)-aryl or—(C₃-C₂₀)-heteroaryl, may each independently be substituted by one ormore of the above-described substituents.

In a preferred embodiment, R⁴, R², R³, R⁴ are each independentlyselected from —(C₁-C₁₂)-alkyl and —(C₃-C₂₀)-heteroaryl;

where at least one of the R¹, R², R³, R⁴ radicals is a—(C₃-C₂₀)-heteroaryl radical;

and R⁴, R², R³, R⁴ may each independently be substituted by one or moreof the above-described substituents.

In one embodiment, at least two of the R¹, R², R³, R⁴ radicals are a—(C₃-C₂₀)-heteroaryl radical.

In one embodiment, the R¹ and R³ radicals are each a—(C₃-C₂₀)-heteroaryl radical and may each independently be substitutedby one or more of the substituents described above.

Preferably, R² and R⁴ are independently selected from —(C₁-C₁₂)-alkyl,—(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —(C₆-C₂₀)-aryl, morepreferably from —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₆-C₂₀)-aryl,most preferably from —(C₁-C₁₂)-alkyl. R² and R⁴ may independently besubstituted by one or more of the above-described substituents.

In one embodiment, the R¹, R², R³ and R⁴ radicals are a—(C₆-C₂₀)-heteroaryl radical and may each independently be substitutedby one or more of the substituents described above.

In one embodiment, the R¹, R², R³ and R⁴ radicals, if they are aheteroaryl radical, are each independently selected from heteroarylradicals having five to ten ring atoms, preferably five or six ringatoms.

In one embodiment, the R¹, R², R³ and R⁴ radicals, if they are aheteroaryl radical, are a heteroaryl radical having five ring atoms.

In one embodiment, the R¹, R², R³ and R⁴ radicals, if they are aheteroaryl radical, are each independently selected from heteroarylradicals having six to ten ring atoms.

In one embodiment, the R¹, R², R³ and R⁴ radicals, if they are aheteroaryl radical, are a heteroaryl radical having six ring atoms.

In one embodiment, the R¹, R², R³ and R⁴ radicals, if they are aheteroaryl radical, are selected from furyl, thienyl, pyrrolyl,oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, imidazolyl, pyrazolyl,furazanyl, tetrazolyl, pyridyl, pyridazinyl, pyrimidyl, pyrazinyl,benzofuranyl, indolyl, isoindolyl, benzimidazolyl, quinolyl,isoquinolyl, where the heteroaryl radicals mentioned may be substitutedas described above.

In one embodiment, the R¹, R², R³ and R⁴ radicals, if they are aheteroaryl radical, are selected from furyl, thienyl, pyrrolyl,imidazolyl, pyridyl, pyrimidyl, indolyl, where the heteroaryl radicalsmentioned may be substituted as described above.

In one embodiment, the R¹, R², R³ and R⁴ radicals, if they are aheteroaryl radical, are selected from 2-furyl, 2-thienyl, 2-pyrrolyl,2-imidazolyl, 2-pyridyl, 2-pyrimidyl, 2-indolyl, where the heteroarylradicals mentioned may be substituted as described above.

In one embodiment, the R¹, R², R³ and R⁴ radicals, if they are aheteroaryl radical, are selected from 2-furyl, 2-thienyl,N-methyl-2-pyrrolyl, N-phenyl-2-pyrrolyl,N-(2-methoxyphenyl)-2-pyrrolyl, 2-pyrrolyl, N-methyl-2-imidazolyl,2-imidazolyl, 2-pyridyl, 2-pyrimidyl, N-phenyl-2-indolyl, 2-indolyl,where the heteroaryl radicals mentioned have no further substitution.

More preferably, the R¹, R², R³ and R⁴ radicals, if they are aheteroaryl radical, are pyridyl, especially 2-pyridyl.

In one embodiment, R¹ and R³ are a pyridyl radical, preferably2-pyridyl, and R² and R⁴ are —(C₁-C₁₂)-alkyl, where R¹, R², R³ and R⁴may each be substituted as described above.

In one embodiment, the diphosphine compounds according to the inventionare a compound of formula (1):

The invention further relates to complexes comprising Pd and adiphosphine compound according to the invention. In these complexes, thediphosphine compound according to the invention serves as a bidentateligand for the metal atom. The complexes serve, for example, ascatalysts for alkoxycarbonylation. With the complexes according to theinvention, it is possible to achieve high yields in thealkoxycarbonylation of a multitude of different ethylenicallyunsaturated compounds.

The complexes according to the invention may also comprise furtherligands which coordinate to the metal atom. These are, for example,ethylenically unsaturated compounds or anions. Suitable additionalligands are, for example, styrene, acetate anions, maleimides (e.g.N-methylmaleimide), 1,4-naphthoquinone, trifluoroacetate anions orchloride anions.

The invention further relates to the use of a diphosphine compoundaccording to the invention for catalysis of an alkoxycarbonylationreaction. The compound according to the invention can especially be usedas a metal complex according to the invention.

The invention also relates to a process comprising the process steps of:

-   a) initially charging an ethylenically unsaturated compound;-   b) adding a diphosphine compound according to the invention and a    compound comprising Pd,    -   or adding a complex according to the invention comprising Pd and        a diphosphine compound according to the invention;-   c) adding an alcohol;-   d) feeding in CO;-   e) heating the reaction mixture, with conversion of the    ethylenically unsaturated compound to an ester.

In this process, process steps a), b), c) and d) can be effected in anydesired sequence. Typically, however, the addition of CO is effectedafter the co-reactants have been initially charged in steps a) to c).Steps d) and e) can be effected simultaneously or successively. Inaddition, CO can also be fed in in two or more steps, in such a waythat, for example, a portion of the CO is first fed in, then the mixtureis heated, and then a further portion of CO is fed in.

The ethylenically unsaturated compounds used as reactant in the processaccording to the invention contain one or more carbon-carbon doublebonds. These compounds are also referred to hereinafter as olefins forsimplification. The double bonds may be terminal or internal.

Preference is given to ethylenically unsaturated compounds having 2 to30 carbon atoms, preferably 2 to 22 carbon atoms, more preferably 2 to12 carbon atoms.

In one embodiment, the ethylenically unsaturated compound comprises 4 to30 carbon atoms, preferably 6 to 22 carbon atoms, more preferably 8 to12 carbon atoms. In a particularly preferred embodiment, theethylenically unsaturated compound comprises 8 carbon atoms.

The ethylenically unsaturated compounds may, in addition to the one ormore double bonds, contain further functional groups. Preferably, theethylenically unsaturated compound comprises one or more functionalgroups selected from carboxyl, thiocarboxyl, sulpho, sulphinyl,carboxylic anhydride, imide, carboxylic ester, sulphonic ester,carbamoyl, sulphamoyl, cyano, carbonyl, carbonothioyl, hydroxyl,sulphhydryl, amino, ether, thioether, aryl, heteroaryl or silyl groupsand/or halogen substituents. At the same time, the ethylenicallyunsaturated compound preferably comprises a total of 2 to 30 carbonatoms, preferably 2 to 22 carbon atoms, more preferably 2 to 12 carbonatoms.

In one embodiment, the ethylenically unsaturated compound does notcomprise any further functional groups apart from carbon-carbon doublebonds.

In a particularly preferred embodiment, the ethylenically unsaturatedcompound is an unfunctionalized alkene having at least one double bondand 2 to 30 carbon atoms, preferably 6 to 22 carbon atoms, furtherpreferably 8 to 12 carbon atoms, and most preferably 8 carbon atoms.

Suitable ethylenically unsaturated compounds are, for example:

ethene;

propene;

C4 olefins such as 1-butene, cis-2-butene, trans-2-butene, mixture ofcis- and trans-2-butene, isobutene, 1,3-butadiene; raffinate I to III,crack-C4

C5 olefins such as 1-pentene, 2-pentene, 2-methyl-1-butene,2-methyl-2-butene, 2-methyl-1,3-butadiene (isoprene), 1,3-pentadiene;

C6 olefins such as tetramethylethylene, 1,3-hexadiene,1,3-cyclohexadiene;

C7 olefins such as 1-methylcyclohexene, 2,4-heptadiene, norbornadiene;

C8 olefins such as 1-octene, 2-octene, cyclooctene, di-n-butene,diisobutene, 1,5-cyclooctadiene, 1,7-octadiene;

C9 olefins such as tripropene;

C10 olefins such as dicyclopentadiene;

undecenes;

dodecenes;

internal C14 olefins;

internal C15 to C18 olefins;

linear or branched, cyclic, acyclic or partly cyclic, internal C15 toC30 olefins;

triisobutene, tri-n-butene;

terpenes such as limonene, geraniol, farnesol, pinene, myrcene, carvone,3-carene; polyunsaturated compounds having 18 carbon atoms, such aslinoleic acid or linolenic acid; esters of unsaturated carboxylic acids,such as vinyl esters of acetic or propionic acid, alkyl esters ofunsaturated carboxylic acids, methyl or ethyl esters of acrylic acid andmethacrylic acid, oleic esters, such as methyl or ethyl oleate, estersof linoleic or linolenic acid; vinyl compounds such as vinyl acetate,vinylcyclohexene, styrene, alpha-methylstyrene,2-isopropenylnaphthalene;

2-methyl-2-pentenal, methyl 3-pentenoate, methacrylic anhydride.

In one variant of the process, the ethylenically unsaturated compound isselected from propene, 1-butene, cis- and/or trans-2-butene, or mixturesthereof.

In one variant of the process, the ethylenically unsaturated compound isselected from 1-pentene, cis- and/or trans-2-pentene, 2-methyl-1-butene,2-methyl-2-butene, 3-methyl-1-butene, or mixtures thereof.

In a preferred embodiment, the ethylenically unsaturated compound isselected from ethene, propene, 1-butene, cis- and/or trans-2-butene,isobutene, 1,3-butadiene, 1-pentene, cis- and/or trans-2-pentene,2-methyl-1-butene, 3-methyl-1-butene, 2-methyl-2-butene, hexene,tetramethylethylene, heptene, n-octene, 1-octene, 2-octene, or mixturesthereof.

In one variant, a mixture of ethylenically unsaturated compounds isused. A mixture in the context of this invention refers to a compositioncomprising at least two different ethylenically unsaturated compounds,where the proportion of each individual ethylenically unsaturatedcompound is preferably at least 5% by weight, based on the total weightof the mixture.

Preference is given to using a mixture of ethylenically unsaturatedcompounds each having 2 to 30 carbon atoms, preferably 4 to 22 carbonatoms, more preferably 6 to 12 carbon atoms, most preferably 8 to 10carbon atoms.

Suitable mixtures of ethylenically unsaturated compounds are thosecalled raffinates I to III. Raffinate I comprises 40% to 50% isobutene,20% to 30% 1-butene, 10% to 20% cis- and trans-2-butene, up to 1%1,3-butadiene and 10% to 20% n-butane and isobutane. Raffinate 11 is aportion of the C₄ fraction which arises in naphtha cracking and consistsessentially of the isomeric n-butenes, isobutane and n-butane afterremoval of isobutene from raffinate I. Raffinate III is a portion of theC₄ fraction which arises in naphtha cracking and consists essentially ofthe isomeric n-butenes and n-butane.

A further suitable mixture is di-n-butene, also referred to as dibutene,DNB or DnB. Di-n-butene is an isomer mixture of C8 olefins which arisesfrom the dimerization of mixtures of 1-butene, cis-2-butene andtrans-2-butene. In industry, raffinate II or raffinate III streams aregenerally subjected to a catalytic oligomerization, wherein the butanespresent (n/iso) emerge unchanged and the olefins present are convertedfully or partly. As well as dimeric di-n-butene, higher oligomers(tributene C12, tetrabutene C16) generally also form, which are removedby distillation after the reaction. These can likewise be used asreactants.

In a preferred variant, a mixture comprising isobutene, 1-butene, cis-and trans-2-butene is used. Preferably, the mixture comprises 1-butene,cis- and trans-2-butene.

The alkoxycarbonylation according to the invention is catalysed by thePd complex according to the invention. The Pd complex may either beadded in process step b) as a preformed complex comprising Pd and thephosphine ligands according to the invention or be formed in situ from acompound comprising Pd and the free phosphine ligand. In this context,the compound comprising Pd is also referred to as catalyst precursor.

In the case that the catalyst is formed in situ, the ligand can be addedin excess, such that the unbound ligand is also present in the reactionmixture.

In one variant, the compound comprising Pd is selected from palladiumchloride (PdCl₂), palladium(II) acetylacetonate [Pd(acac)₂],palladium(II) acetate [Pd(OAc)₂],dichloro(1,5-cyclooctadiene)palladium(II) [Pd(cod)₂Cl₂],bis(dibenzylideneacetone)palladium [Pd(dba)₂],bis(acetonitrile)dichloropalladium(II) [Pd(CH₃CN)₂Cl₂],palladium(cinnamyl) dichloride [Pd(cinnamyl)Cl₂].

Preferably, the compound comprising Pd is PdCl₂, Pd(acac)₂ or Pd(OAc)₂.PdCl₂ is particularly suitable.

The alcohol in process step c) may be branched or linear, cyclic,alicyclic, partly cyclic or aliphatic, and is especially a C₁- toC₃₀-alkanol. It is possible to use monoalcohols or polyalcohols.

The alcohol in process step c) comprises preferably 1 to 30 carbonatoms, more preferably 1 to 22 carbon atoms, especially preferably 1 to12 carbon atoms. It may be a monoalcohol or a polyalcohol.

The alcohol may, in addition to the one or more hydroxyl groups, containfurther functional groups. Preferably, the alcohol may additionallycomprise one or more functional groups selected from carboxyl,thiocarboxyl, sulpho, sulphinyl, carboxylic anhydride, imide, carboxylicester, sulphonic ester, carbamoyl, sulphamoyl, cyano, carbonyl,carbonothioyl, sulphhydryl, amino, ether, thioether, aryl, heteroaryl orsilyl groups and/or halogen substituents.

In one embodiment, the alcohol does not comprise any further functionalgroups except for hydroxyl groups.

The alcohol may contain unsaturated and aromatic groups. However, it ispreferably an aliphatic alcohol.

An aliphatic alcohol in the context of this invention refers to analcohol which does not comprise any aromatic groups, i.e., for example,an alkanol, alkenol or alkynol. Unsaturated nonaromatic alcohols arethus also permitted.

In one embodiment, the alcohol is an alkanol having one or more hydroxylgroups and 1 to 30 carbon atoms, preferably 1 to 22 carbon atoms, morepreferably 1 to 12 carbon atoms, most preferably 1 to 6 carbon atoms.

In one variant of the process, the alcohol in process step c) isselected from the group of the monoalcohols.

In one variant of the process, the alcohol in process step c) isselected from: methanol, ethanol, 1-propanol, isopropanol, isobutanol,tert-butanol, 1-butanol, 2-butanol, 1-pentanol, 2-pentanol, 3-pentanol,1-hexanol, cyclohexanol, phenol, 2-ethylhexanol, isononanol,2-propylheptanol.

In a preferred variant, the alcohol in process step c) is selected frommethanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, 1-hexanol,2-propanol, tert-butanol, 3-pentanol, cyclohexanol, phenol, and mixturesthereof.

In one variant of the process, the alcohol in process step c) isselected from the group of the polyalcohols.

In one variant of the process, the alcohol in process step c) isselected from: diols, triols, tetraols.

In one variant of the process, the alcohol in process step c) isselected from: cyclohexane-1,2-diol, ethane-1,2-diol, propane-1,3-diol,glycerol, butane-1,2,4-triol, 2-hydroxymethylpropane-1,3-diol,1,2,6-trihydroxyhexane, pentaerythritol, 1,1,1-tri(hydroxymethyl)ethane,catechol, resorcinol and hydroxyhydroquinone.

In one variant of the process, the alcohol in process step c) isselected from: sucrose, fructose, mannose, sorbose, galactose andglucose.

In a preferred embodiment of the process, the alcohol in process step c)is selected from methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol,1-hexanol.

In a particularly preferred variant of the process, the alcohol inprocess step c) is selected from: methanol, ethanol.

In a particularly preferred variant of the process, the alcohol inprocess step c) is methanol.

In one variant of the process, the alcohol in process step c) is used inexcess.

In one variant of the process, the alcohol in process step c) is usedsimultaneously as solvent.

In one variant of the process, a further solvent is used, selected from:toluene, xylene, tetrahydrofuran (THF) and methylene chloride (CH₂Cl₂).

CO is fed in in step d) preferably at a partial CO pressure between 0.1and 10 MPa (1 to 100 bar), preferably between 1 and 8 MPa (10 to 80bar), more preferably between 2 and 4 MPa (20 to 40 bar).

The reaction mixture is heated in step e) of the process according tothe invention preferably to a temperature between 10° C. and 180° C.,preferably between 20 and 160° C., more preferably between 40 and 120°C., in order to convert the ethylenically unsaturated compound to anester.

The molar ratio of the ethylenically unsaturated compound initiallycharged in step a) to the alcohol added in step c) is preferably between1:1 and 1:20, more preferably 1:2 to 1:10, more preferably 1:3 to 1:4.

The mass ratio of Pd to the ethylenically unsaturated compound initiallycharged in step a) is preferably between 0.001% and 0.5% by weight,preferably between 0.01% and 0.1% by weight, more preferably between0.01% and 0.05% by weight.

The molar ratio of the diphosphine compound according to the inventionto Pd is preferably between 0.1:1 and 400:1, preferably between 0.5:1and 400:1, more preferably between 1:1 and 100:1, most preferablybetween 2:1 and 50:1.

Preferably, the process is conducted with addition of an acid. In onevariant, the process therefore additionally comprises step c′): addingan acid to the reaction mixture. This may preferably be a Brønsted orLewis acid.

Suitable Brønsted acids preferably have an acid strength of pK_(a)≤5,preferably an acid strength of pK_(a)≤3. The reported acid strengthpK_(a) is based on the pK_(a) determined under standard conditions (25°C., 1.01325 bar). In the case of a polyprotic acid, the acid strengthpK_(a) in the context of this invention relates to the pK_(a) of thefirst protolysis step.

Preferably, the acid is not a carboxylic acid.

Suitable Brønsted acids are, for example, perchloric acid, sulphuricacid, phosphoric acid, methylphosphonic acid and sulphonic acids.Preferably, the acid is sulphuric acid or a sulphonic acid. Suitablesulphonic acids are, for example, methanesulphonic acid,trifluoromethanesulphonic acid, tert-butanesulphonic acid,p-toluenesulphonic acid (PTSA), 2-hydroxypropane-2-sulphonic acid,2,4,6-trimethylbenzenesulphonic acid and dodecylsulphonic acid.Particularly preferred acids are sulphuric acid, methanesulphonic acid,trifluoromethanesulphonic acid and p-toluenesulphonic acid.

A Lewis acid used may, for example, be aluminium triflate.

In one embodiment, the amount of acid added in step c′) is 0.3 to 40 mol%, preferably 0.4 to 15 mol %, more preferably 0.5 to 5 mol %, mostpreferably 0.6 to 3 mol %, based on the molar amount of theethylenically unsaturated compound used in step a).

EXAMPLES

The examples which follow illustrate the invention.

General Procedures

All the preparations which follow were carried out under protective gasusing standard Schlenk techniques. The solvents were dried over suitabledesiccants before use (Purification of Laboratory Chemicals, W. L. F.Armarego (Author), Christina Chai (Author), Butterworth Heinemann(Elsevier), 6th edition, Oxford 2009).

Phosphorus trichloride (Aldrich) was distilled under argon before use.All preparative operations were effected in baked-out vessels. Theproducts were characterized by means of NMR spectroscopy. Chemicalshifts (6) are reported in ppm. The ³¹P NMR signals were referenced asfollows: SR_(31P)═SR_(1H)*(BF_(31P)/BF_(1H))═SR_(1H)*0.4048. (Robin K.Harris, Edwin D. Becker, Sonia M. Cabral de Menezes, Robin Goodfellow,and Pierre Granger, Pure Appl. Chem., 2001, 73, 1795-1818; Robin K.Harris, Edwin D. Becker, Sonia M. Cabral de Menezes, Pierre Granger, RoyE. Hoffman and Kurt W. Zilm, Pure Appl. Chem., 2008, 80, 59-84).

The recording of nuclear resonance spectra was effected on Bruker Avance300 or Bruker Avance 400, gas chromatography analysis on Agilent GC7890A, elemental analysis on Leco TruSpec CHNS and Varian ICP-OES 715,and ESI-TOF mass spectrometry on Thermo Electron Finnigan MAT 95-XP andAgilent 6890 N/5973 instruments.

Preparation of chloro-2-pyridyl-tert-butylphosphine (Precursor A)

The Grignard for the synthesis of chloro-2-pyridyl-t-butylphosphine isprepared by the “Knochel method” with isopropylmagnesium chloride(Angew. Chem. 2004, 43, 2222-2226). The workup is effected according tothe method of Budzelaar (Organometallics 1990, 9, 1222-1227).

8.07 ml of a 1.3 M isopropylmagnesium chloride solution (Knochel'sreagent) are introduced into a 50 ml round-bottom flask with magneticstirrer and septum, and cooled to −15° C. Thereafter, 953.5 μl (10 mmol)of 2-bromopyridine are rapidly added dropwise. The solution immediatelyturns yellow. It is allowed to warm up to −10° C. The conversion of thereaction is determined as follows: about 100 μl solution are taken andintroduced into 1 ml of a saturated ammonium chloride solution. If thesolution “bubbles”, not much Grignard has formed yet. The aqueoussolution is extracted with a pipette of ether and the organic phase isdried over Na₂SO₄. A GC of the ethereal solution is recorded. When alarge amount of pyridine has formed compared to 2-bromopyridine,conversions are high. At −10° C., there has been little conversion.After warming up to room temperature and stirring for 1-2 hours, thereaction solution turns brown-yellow. A GC test shows completeconversion. Now the Grignard solution can be slowly added dropwise witha syringe pump to a solution of 1.748 g (11 mmol) ofdichloro-tert-butylphosphine in 10 ml of THF which has been cooled to−15° C. beforehand. It is important that thedichloro-tert-butylphosphine solution is cooled. At room temperature,considerable amounts of dipyridyl-tert-butylphosphine would be obtained.A clear yellow solution is initially formed, which then turns cloudy.The mixture is left to warm up to room temperature and to stirovernight. According to GC-MS, a large amount of product has formed. Thesolvent is removed under high vacuum and a whitish solid which is brownin places is obtained. The solid is suspended with 20 ml of heptane andthe solid is comminuted in an ultrasound bath. After allowing the whitesolid to settle out, the solution is decanted. The operation is repeatedtwice with 10-20 ml each time of heptane. After concentration of theheptane solution under high vacuum, it is distilled under reducedpressure. At 4.6 mbar, oil bath 120° C. and distillation temperature 98°C., the product can be distilled. 1.08 g of a colourless oil areobtained. (50%).

Analytical data: ¹H NMR (300 MHz, C₆D₆): δ 8.36 (m, 1H, Py), 7.67 (m,1H, Py), 7.03-6.93 (m, 1H, Py), 6.55-6.46 (m, 1H, Py), 1.07 (d, J=13.3Hz, 9H, t-Bu).

¹³C NMR (75 MHz, C₆D₆): δ 162.9, 162.6, 148.8, 135.5, 125.8, 125.7,122.8, 35.3, 34.8, 25.9 and 25.8.

³¹P NMR (121 MHz, C₆D₆) δ 97.9.

MS (EI) m:z (relative intensity) 201 (M*, 2), 147(32), 145 (100), 109(17), 78 (8), 57.1 (17).

Preparation of Compound 1

675 mg (27.8 mmol, 4 equivalents) of Mg powder are weighed out in aglovebox in a 250 ml round-bottom flask with a nitrogen tap and magneticstirrer bar, and the flask is sealed with a septum. High vacuum isapplied to the round-bottom flask (about 5×10⁻² mbar) and it is heatedto 90° C. for 45 minutes. After cooling down to room temperature, 2grains of iodine are added and the mixture is dissolved in 20 ml of THF.The suspension is stirred for about 10 minutes until the yellow colourof the iodine has disappeared. After the magnesium powder has settledout, the cloudy THF solution is decanted and the activated magnesiumpowder is washed twice with 1-2 ml of THF. Then another 20 ml of freshTHF are added. At room temperature, a solution of 755.5 μl (6.9 mmol) of1,4-dichlorobutane in 70 ml of THF is slowly added dropwise with asyringe pump. The THF solution is clear and pale yellow. The next day,the solution is dark grey but clear and is filtered through Celite. Asample of the Grignard solution is quenched and examined in GC asfollows:

300 μl of Grignard solution is quenched with 1 ml of a saturated aqueoussolution of NH₄Cl and extracted with ether. After drying over Na₂SO₄, aGC of the ether solution is recorded. 1,4-Dichlorobutane is no longerdetectable, but the butane formed cannot be observed in the GC.

The content of Grignard compound is determined as follows:

1 ml of Grignard solution is quenched with 3 ml of 0.1 M HCl and theexcess acid is titrated with 0.1 M NaOH. A suitable indicator is anaqueous 0.04% bromocresol solution. The colour change goes from yellowto blue. 1.70 ml of 0.1 M NaOH has been consumed. 3 ml−1.70 ml=1.3 ml,corresponding to 0.13 mmol of Grignard compound. Since a di-Grignard ispresent, the Grignard solution is 0.065 M.

Based on 90 ml of solution this is 85% of Grignard solution. TheGrignard can now be reacted with the chlorophosphine:

In a 250 ml three-neck flask with reflux condenser, magnetic stirrer barand nitrogen tap, under argon, 1.94 g (9.75 mmol, 2.5 eq) ofchloro-2-pyridyl-t-butylphosphine (precursor A) are dissolved in 10 mlof THF and cooled to −60° C. Then 60 ml of the above-stipulated Grignardsolution (0.065 M, 3.9 mmol) are slowly added dropwise at thistemperature with a syringe pump. The solution at first remains clear andthen turns intense yellow. The mixture is left to warm up to roomtemperature overnight and a clear yellow solution is obtained. Tocomplete the reaction, the mixture is heated under reflux for 2 hours.After cooling, 1 ml of H₂O is added and the solution loses colour and awhite solid precipitates out. After removing THE under high vacuum, astringy, pale yellow solid is obtained. 15 ml of water and 20 ml ofether are added thereto, and two homogeneous clear phases are obtained,which have good separability. The aqueous phase is extracted twice withether. After the organic phase has been dried with Na₂SO₄, the ether isremoved under high vacuum and a viscous, almost colourless oil isobtained. The latter is dissolved in 4 ml of MeOH while heating on awater bath and filtered through Celite. At −28° C., 660 mg of productare obtained in the form of white tacky crystals overnight. (44%).

¹H NMR (300 MHz, C₆D₆): δ 8.54 (m, 2H, py), 7.37 (m, 2H, py), 6.96 (m,2H, Py), 6.58 (m, 2H, Py), 2.68 (m, 2H, CH₂), 1.74 (m, 4H, CH₂), 1.52(m; 2H, CH₂), 1.03 (d, J=11.5 Hz, 18H, tBu).

¹³C NMR (75 MHz, C₆D₆): δ 162.8, 162.5 (q), 149.9, 134.3, 134.1, 132.0,131.5 and 122.4 (py), 29.4, 29.3, 29.1, 29.0, 20.7, 20.5 (CH₂), 28.1 and27.9 (tBu).

³¹P NMR (121 MHz, C₆D₆) δ 8.2.

HRMS (ESI) m/z⁺ calculated for: C₂₂H₃₄N₂P₂ (M+H)⁺389.227; found:389.2273.

EA calculated for: C₂₂H₃₄N₂P₂: C, 68.02; H, 8.82; N, 7.21; P, 15.95.found: C, 68.16; H, 8.97; N, 7.07; P, 15.91.

Preparation of bis(diadamantylphosphinbutane Borane Adduct) (PrecursorB)

In a 100 ml round-bottom flask with nitrogen tap and magnetic stirrerbar, 214.7 mg (0.679 mmol) of diadamantylphosphine borane adduct areweighed out. The flask is closed with a septum and, after purging withargon, 10 ml of THF are added. The borane adduct has good solubility inTHF, and a clear colourless solution is obtained, which is cooled to−78° C. with dry ice. After stirring for 15 minutes, 0.5 ml (0.70 mmol)of a 1.4 M sec-BuLi solution is slowly added dropwise. After thedropwise addition, a pale yellowish, clear solution is obtained, whichis brought to room temperature within 3 hours. The still pale yellowishsolution is left to stir at room temperature for a further hour and thesolution is cooled back to −78° C. Then 42.6 μl (0.323 mmol) ofdiiodobutane diluted with 5 ml of THF are slowly added dropwise to thissolution. The yellow solution loses colour in the process. The mixtureis left to warm up overnight, and a large amount of white solidprecipitates out. 8 ml of water are added and the mixture is stirredvigorously for 20 minutes. Further solid floats on top of the solution.The solution is decanted and the white solid is washed three times withMeOH in order to remove any water still present. After drying underreduced pressure, a yield of 210 mg (95%) of a white solid is obtained.

¹H NMR (300 MHz, CDCl₃): δ 2.11-1.89 (m, 36H, Ad), 1.79-1.68 (m, 24H,Ad), 1.67-1.49 (m, 8H, CH₂), 1.03-(−0.51) (m, broad), 6H, BH₃).

¹³C NMR (75 MHz, CDCl₃): δ 37.8 and 36.6 (Ad), 36.5 and 36.4 (C), 28.1and 28.0 (Ad), 27.9, 27.7, 15.1 and 14.7 ((CH₂)₄).

³¹P NMR (121 MHz, CDCl₃) δ 36.6-33.4 (m).

Preparation of Diadamantylphosphine Borane Adduct (Precursor C)

4.0 g (13.22 mmol) of diadamantylphosphine are weighed out in a 100 mlround bottom flask with nitrogen tap and oval magnetic stirrer bar,closed with a septum and purged. The solid is suspended in 9 ml of THFand 18.9 ml (18.9 mmol, 1 M) of BH₃-THF adduct are added rapidly to thissuspension. The suspension at first begins to dissolve. After a while,however, a white solid precipitates out. The mixture is left to stirovernight and the THF is removed under high vacuum. The white residue istaken up in 250 ml of ethyl acetate while heating (60° C.) on a waterbath. The borane adduct has good solubility in the warm ethyl acetate.After addition of 6 spoonfuls of silica gel 60 (about 12 g), the solventis removed completely on a rotary evaporator and the product which hasbeen absorbed on silica gel is chromatographed with a Combi-Flashapparatus. The eluent used is 1:10 (ethyl acetate/heptane). 3.1 g (74%)of diadamantylphosphine borane adduct are obtained.

¹H NMR (300 MHz, CDCl₃): δ 3.71 (dq, 350.8 Hz and 6.6 Hz, 1H, PH),2.01-1.94 (m, 18H, Ad), 1.74 (m, 12H, Ad), 1.05-(−0.35) (m, 3H, BH₃).

¹³C NMR (75 MHz, CDCl₃): δ 37.9 and 36.4 (CH₂), 34.8 and 34.4 (C), 28.1and 28.0 (CH).

³¹P NMR (121 MHz, CDCl₃) δ 42.8-40.0 (m).

Preparation of ligand 2: bis(diadamantylphosphino)butane (ComparativeLigand)

500 mg (0.728 mmol) of borane adduct are weighed out in a 25 mlround-bottom flask with nitrogen tap, and 10 ml of absolute pyrrolidineare added. The suspension is heated under reflux until the solution iscolourless and clear (about 2 h). After cooling, the pyrrolidine isremoved under high vacuum and a white residue was obtained. This istaken up in 15 ml of toluene and heated to 90° C. The almost clearsolution is difficult to filter, since the product precipitates outagain in the course of cooling. A white crystalline solid precipitatesout of the filtrate in the refrigerator (3° C.). Crystals are washedtwice with toluene and dried under high vacuum. 300 mg (62%) of whitecrystals are obtained.

Owing to poor solubility at room temperature, a 1H, 13C and 31P NMR inbenzene-d6 is recorded at 323 K.

¹H NMR (323 K, 400 MHz, C₆D₆): δ 2.12-1.92 (m, 16H, CH₂, Ad), 1.92-1.79(m, 11H, CH₂, Ad), 1.75-1.64 (m, 16H, CH₂, Ad), 1.64-1.47 (m, 6H, CH₂,Ad), 1.45-1.23 (m, 18H, CH₂, Ad).

¹³C NMR (323 K, 100 MHz, C₆D₆): δ 41.5 and 41.4 (Ad), 37.5 (Ad), 36.5and 36.3 (C), 30.1 (CH₂), 29.3 and 29.2 (Ad), 17.5 and 17.3 (CH₂).

³¹P NMR (323 K, 162 MHz, C₆D₆) δ 25.71.

High-Pressure Experiments

Feedstocks:

Di-n-butene was also referred to as follows: dibutene, DNB or DnB.

Di-n-butene is an isomer mixture of C8 olefins which arises from thedimerization of mixtures of 1-butene, cis-2-butene and trans-2-butene.In industry, raffinate II or raffinate Ill streams are generallysubjected to a catalytic oligomerization, wherein the butanes present(n/iso) emerge unchanged and the olefins present are converted fully orpartly. As well as dimeric di-n-butene, higher oligomers (tributene C12,tetrabutene C16) generally also form, which have to be removed bydistillation after the reaction.

Another process practised in industry for oligomerization of C4 olefinsis called the “OCTOL process”.

Within the patent literature, DE102008007081A1, for example, describesan oligomerization based on the OCTOL process. EP1029839A1 is concernedwith the fractionation of the C8 olefins formed in the OCTOL process.

Technical di-n-butene consists generally to an extent of 5% to 30% ofn-octenes, 45% to 75% of 3-methylheptenes, and to an extent of 10% to35% of 3,4-dimethylhexenes. Preferred streams contain 10% to 20%n-octenes, 55% to 65% 3-methylheptenes, and 15% to 25%3,4-dimethylhexenes.

para-Toluenesulphonic acid was abbreviated as follows: pTSA, PTSA orp-TSA. PTSA in this text always refers to para-toluenesulphonic acidmonohydrate.

General Method for Performance of the High-Pressure Experiments

General experimental method for autoclave experiments in glass vials:

A 300 ml Parr reactor is used. Matched to this is an aluminium block ofcorresponding dimensions which has been manufactured in-house and whichis suitable for heating by means of a conventional magnetic stirrer, forexample from Heidolph. For the inside of the autoclave, a round metalplate of thickness about 1.5 cm was manufactured, containing 6 holescorresponding to the external diameter of the glass vials. Matchingthese glass vials, they are equipped with small magnetic stirrers. Theseglass vials are provided with screw caps and suitable septa and charged,using a special apparatus manufactured by glass blowers, under argonwith the appropriate reactants, solvents and catalysts and additives.For this purpose, 6 vessels are filled at the same time; this enablesthe performance of 6 reactions at the same temperature and the samepressure in one experiment. Then these glass vessels are closed withscrew caps and septa, and a small syringe cannula of suitable size isused to puncture each of the septa. This enables gas exchange later inthe reaction. These vials are then placed in the metal plate and theseare transferred into the autoclave under argon. The autoclave is purgedwith CO and filled at room temperature with the CO pressure intended.Then, by means of the magnetic stirrer, under magnetic stirring, theautoclave is heated to reaction temperature and the reaction isconducted for the appropriate period. Subsequently, the autoclave iscooled down to room temperature and the pressure is slowly released.Subsequently, the autoclave is purged with nitrogen. The vials are takenfrom the autoclave, and a defined amount of a suitable standard isadded. A GC analysis is effected, the results of which are used todetermine yields and selectivities.

Analysis

GC analysis of di-n-butene: for the GC analysis, an Agilent 7890A gaschromatograph having a 30 m HP5 column is used. Temperature profile: 35°C., 10 min; 10° C./min to 200° C.; the injection volume is 1 μl with asplit of 50:1.

Retention times for di-n-butene and products: 10.784-13.502 min Theesters formed from di-n-butene are referred to hereinafter as MINO(methyl isononanoate).

Retention time for ether products of unknown isomer distribution:15.312, 17.042, 17.244, 17.417 min

Retention time for iso-C9 esters 19.502-20.439 min (main peak: 19.990min)

Retention time for n-C9 esters: 20.669, 20.730, 20.884, 21.266 min.

Evaluation of the Experiments

For the evaluation of the catalytic experiments, particular indicatorswhich permit comparison of the various catalyst systems are usedhereinafter.

TON: turnover number, defined as moles of product per mole of catalystmetal, is a measure of the productivity of the catalytic complex.

TOF: turnover frequency, defined as TON per unit time for the attainmentof a particular conversion, e.g. 50%. The TOF is a measure of theactivity of the catalytic system.

The n selectivities reported hereinafter relate to the proportion ofterminal methoxycarbonylation based on the overall yield ofmethoxycarbonylation products.

The n/iso ratio indicates the ratio of olefins converted terminally toesters to olefins converted internally to esters.

Methoxycarbonylation of di-n-butene

Ligand 2 (comparative example): A 25 ml Schlenk vessel was charged witha stock solution of [Pd(acac)₂] (1.95 mg, 6.4 μmol), p-toluenesulphonicacid (PTSA) (18.24 mg, 95.89 μmol) and MeOH (10 ml). A 4 ml vial wascharged with 2 (2.11 mg, 0.16 mol % based on the molar amount ofdi-n-butene), and a magnetic stirrer bar was added. Thereafter, 1.25 mlof the clear yellow stock solution and di-n-butene (315 μl, 2 mmol) wereadded with a syringe. The molar proportions based on the molar amount ofdi-n-butene are thus 0.04 mol % for Pd(acac)₂ and 0.6 mol % for PTSA.The vial was placed into a sample holder which was in turn inserted intoa 300 ml Parr autoclave under an argon atmosphere. After the autoclavehad been purged three times with nitrogen, the CO pressure was adjustedto 40 bar. The reaction proceeded at 120° C. for 20 hours. On conclusionof the reaction, the autoclave was cooled down to room temperature andcautiously decompressed. Isooctane was added as internal GC standard.Yield and regioselectivity were determined by means of GC. No MINOformation was observed.

Ligand 1: A 25 ml Schlenk vessel was charged with a stock solution of[Pd(acac)₂] (1.95 mg, 6.4 μmol), p-toluenesulphonic acid (PTSA) (18.24mg, 95.89 μmol) and MeOH (10 ml). A 4 ml vial was charged with 1 (1.24mg, 0.16 μmol % based on the molar amount of di-n-butene), and amagnetic stirrer bar was added. Thereafter, 1.25 ml of the clear yellowstock solution and di-n-butene (315 μl, 2 mmol) were added with asyringe. The molar proportions based on the molar amount of di-n-buteneare thus 0.04 mol % for Pd(acac)₂ and 0.6 mol % for PTSA. The vial wasplaced into a sample holder which was in turn inserted into a 300 mlParr autoclave under an argon atmosphere. After the autoclave had beenpurged three times with nitrogen, the CO pressure was adjusted to 40bar. The reaction proceeded at 120° C. for 20 hours. On conclusion ofthe reaction, the autoclave was cooled down to room temperature andcautiously decompressed. Isooctane was added as internal GC standard.Yield and regioselectivity were determined by means of GC. (MINO yield:13%, n/iso regioselectivity: 59/41).

This experiment shows that the inventive ligand 1 forms a catalyticallyactive palladium complex which catalyses the alkoxycarbonylation ofdi-n-butene. The structurally similar ligand 2, by contrast, isunsuitable for catalysing alkoxycarbonylation.

1. Compound of formula (I)

where R¹, R², R³, R⁴ are each independently selected from—(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl,—(C₆-C₂₀)-aryl, —(C₃-C₂₀)-heteroaryl; at least one of the R¹, R², R³, R⁴radicals is a —(C₃-C₂₀)-heteroaryl radical; and R¹, R², R³, R⁴, if theyare —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl,—(C₆-C₂₀)-aryl or —(C₃-C₂₀)-heteroaryl, may each independently besubstituted by one or more substituents selected from —(C₁-C₁₂)-alkyl,—(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —O—(C₁-C₁₂)-alkyl,—O—(C₁-C₁₂)-alkyl-(C₆-C₂₀)-aryl, —O—(C₃-C₁₂)-cycloalkyl,—S—(C₁-C₁₂)-alkyl, —S—(C₃-C₁₂)-cycloalkyl, —COO—(C₁-C₁₂)-alkyl,—COO—(C₃-C₁₂)-cycloalkyl, —CONH—(C₁-C₁₂)-alkyl,—CONH—(C₃-C₁₂)-cycloalkyl, —CO—(C₁-C₁₂)-alkyl, —CO—(C₃-C₁₂)-cycloalkyl,—N—[(C₁-C₁₂)-alkyl]₂, —(C₆-C₂₀)-aryl, —(C₆-C₂₀)-aryl-(C₁-C₁₂)-alkyl,—(C₆-C₂₀)-aryl-O—(C₁-C₁₂)-alkyl, —(C₃-C₂₀)-heteroaryl,—(C₃-C₂₀)-heteroaryl-(C₁-C₁₂)-alkyl,—(C₃-C₂₀)-heteroaryl-O—(C₁-C₁₂)-alkyl, —COOH, —OH, —SO₃H, —NH₂, halogen.2. Compound according to claim 1, where at least two of the R¹, R², R³,R⁴ radicals are a —(C₃-C₂₀)-heteroaryl radical.
 3. Compound according toclaim 1, where the R¹ and R³ radicals are each a —(C₃-C₂₀)-heteroarylradical.
 4. Compound according to claim 1, where the R¹ and R³ radicalsare each a —(C₃-C₂₀)-heteroaryl radical; and R² and R⁴ are eachindependently selected from —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl,—(C₃-C₁₂)-heterocycloalkyl, —(C₆-C₂₀)-aryl.
 5. Compound according toclaim 1, where the R¹ and R³ radicals are each a —(C₃-C₂₀)-heteroarylradical; and R² and R⁴ are each a —(C₁-C₁₂)-alkyl radical.
 6. Compoundaccording to claim 1, where R¹, R², R³, R⁴, if they are a heteroarylradical, are each independently selected from furyl, thienyl, pyrrolyl,oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, imidazolyl, pyrazolyl,furazanyl, tetrazolyl, pyridyl, pyridazinyl, pyrimidyl, pyrazinyl,benzofuranyl, indolyl, isoindolyl, benzimidazolyl, quinolyl,isoquinolyl.
 7. Compound according to claim 1, of the formula (1)


8. Complex comprising Pd and a compound according to claim
 1. 9. Processcomprising the following process steps: a) initially charging anethylenically unsaturated compound; b) adding a compound of formula (I)

where R¹, R², R³, R⁴ are each independently selected from—(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl,—(C₆-C₂₀)-aryl, —(C₃-C₂₀)-heteroaryl; at least one of the R¹, R², R³, R⁴radicals is a —(C₃-C₂₀)-heteroaryl radical; and R¹, R², R³, R⁴, if theyare —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl,—(C₆-C₂₀)-aryl or —(C₃-C₂₀)-heteroaryl, may each independently besubstituted by one or more substituents selected from —(C₁-C₁₂)-alkyl,—(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —O—(C₁-C₁₂)-alkyl,—O—(C₁-C₁₂)-alkyl-(C₆-C₂₀)-aryl, —O—(C₃-C₁₂)-cycloalkyl,—S—(C₁-C₁₂)-alkyl, —S—(C₃-C₁₂)-cycloalkyl, —COO—(C₁-C₁₂)-alkyl,—COO—(C₃-C₁₂)-cycloalkyl, —CONH—(C₁-C₁₂)-alkyl,—CONH—(C₃-C₁₂)-cycloalkyl, —CO—(C₁-C₁₂)-alkyl, —CO—(C₃-C₁₂)-cycloalkyl,—N—[(C₁-C₁₂)-alkyl]₂, —(C₆-C₂₀)-aryl, —(C₆-C₂₀)-aryl-(C₁-C₁₂)-alkyl,—(C₆-C₂₀)-aryl-O—(C₁-C₁₂)-alkyl, —(C₃-C₂₀)-heteroaryl,—(C₃-C₂₀)-heteroaryl-(C₁-C₁₂)-alkyl,—(C₃-C₂₀)-heteroaryl-O—(C₁-C₁₂)-alkyl, —COOH, —OH, —SO₃H, —NH₂, halogenand a compound comprising Pd, or adding a complex according to claim 8;c) adding an alcohol; d) feeding in CO; e) heating the reaction mixture,with conversion of the ethylenically unsaturated compound to an ester.10. Process according to claim 9, wherein the ethylenically unsaturatedcompound comprises 2 to 30 carbon atoms and optionally one or morefunctional groups selected from carboxyl, thiocarboxyl, sulpho,sulphinyl, carboxylic anhydride, imide, carboxylic ester, sulphonicester, carbamoyl, sulphamoyl, cyano, carbonyl, carbonothioyl, hydroxyl,sulphhydryl, amino, ether, thioether, aryl, heteroaryl or silyl groupsand/or halogen substituents.
 11. Process according to claim 9, whereinthe ethylenically unsaturated compound is selected from ethene, propene,1-butene, cis- and/or trans-2-butene, isobutene, 1,3-butadiene,1-pentene, cis- and/or trans-2-pentene, 2-methyl-1-butene,3-methyl-1-butene, 2-methyl-2-butene, hexene, tetramethylethylene,heptene, 1-octene, 2-octene, di-n-butene, and mixtures thereof. 12.Process according to claim 9, wherein the ethylenically unsaturatedcompound comprises 6 to 22 carbon atoms.
 13. Process according to claim9, wherein the compound comprising Pd in process step b) is selectedfrom palladium dichloride, palladium(II) acetylacetonate, palladium(II)acetate, dichloro(1,5-cyclooctadiene)palladium(II),bis(dibenzylideneacetone)palladium,bis(acetonitrile)dichloropalladium(II), palladium(cinnamyl) dichloride.14. Process according to claim 9, wherein the alcohol in process step c)is selected from methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol,1-hexanol, 2-propanol, tert-butanol, 3-pentanol, cyclohexanol, phenol,and mixtures thereof.
 15. A process for catalysis of analkoxycarbonylation reaction, comprising: introducing a compound offormula (I)

where R¹, R², R³, R⁴ are each independently selected from—(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl,—(C₆-C₂₀)-aryl, —(C₃-C₂₀)-heteroaryl; at least one of the R¹, R², R³, R⁴radicals is a —(C₃-C₂₀)-heteroaryl radical; and R¹, R², R³, R⁴, if theyare —(C₁-C₁₂)-alkyl, —(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl,—(C₆-C₂₀)-aryl or —(C₃-C₂₀)-heteroaryl, may each independently besubstituted by one or more substituents selected from —(C₁-C₁₂)-alkyl,—(C₃-C₁₂)-cycloalkyl, —(C₃-C₁₂)-heterocycloalkyl, —O—(C₁-C₁₂)-alkyl,—O—(C₁-C₁₂)-alkyl-(C₆-C₂₀)-aryl, —O—(C₃-C₁₂)-cycloalkyl,—S—(C₁-C₁₂)-alkyl, —S—(C₃-C₁₂)-cycloalkyl, —COO—(C₁-C₁₂)-alkyl,—COO—(C₃-C₁₂)-cycloalkyl, —CONH—(C₁-C₁₂)-alkyl,—CONH—(C₃-C₁₂)-cycloalkyl, —CO—(C₁-C₁₂)-alkyl, —CO—(C₃-C₁₂)-cycloalkyl,—N—[(C₁-C₁₂)-alkyl]₂, —(C₆-C₂₀)-aryl, —(C₆-C₂₀)-aryl-(C₁-C₁₂)-alkyl,—(C₆-C₂₀)-aryl-O—(C₁-C₁₂)-alkyl, —(C₃-C₂₀)-heteroaryl,—(C₃-C₂₀)-heteroaryl-(C₁-C₁₂)-alkyl,—(C₃-C₂₀)-heteroaryl-O—(C₁-C₁₂)-alkyl, —COOH, —OH, —SO₃H, —NH₂, halogenor a complex according to claim 8.